An extender is usually 2 to 4 inches in length and has opposing clasps on each end, or a ring on one end and clasp on the other.

You simply attach the clasp of the extender to the opposing clasp of the necklace on each side and you're good to go.

You can use purchased chain for the extender or make your own lengths. I usually do the latter since I like to be able to quickly change the length of the extender by removing a link or two.

I make extenders and leave them in the boutiques that sell my jewelry. I also take them with me to art shows where I vend. These little jewels have saved many a sale. I have some regular customers who depend on my willingness to lengthen their necklaces in this manner. If the customer doesn't want to use an extender, I can steal the length of chain from one and permanently lengthen the necklace. It works great.

The extenders in the photo are copper; however, I like to keep both copper and sterling silver extenders available for use. Be prepared for customer preferences.